Abstract: Expressway subgrades constructed in permafrost regions are highly susceptible to deformation and distress under repeated freeze-thaw cycling, particularly in environments characterized by severe climate and poor engineering-geological conditions. To address the subgrade problems observed along the permafrost sections of the Gongyu Expressway during operation, this study investigates crushed-rock ventilated subgrade gravel and stone-slag cushion materials through a combination of field surveys and laboratory testing. The mechanical behavior, soluble-salt content, capillary rise characteristics, permeability, and frost-heave response of the materials were systematically evaluated. The results indicate that the crushed-rock ventilated subgrade fill exhibits favorable gradation that complies with design specifications for permafrost regions. The soluble-salt content (0.057%~0.080%) exerts negligible influence on soil structure and frost-heave potential. The measured capillary rise height (26.0~29.0 cm) and strong capillary rise height (9.9~12.1 cm) both satisfy the performance requirements for permafrost-region subgrades. However, material saturation significantly reduces subgrade stability and may induce multiple forms of distress. These findings provide a scientific basis for evaluating and improving the long-term stability of expressway subgrades in permafrost environments and offer technical support for the maintenance and safe operation of the Gongyu Expressway.

Key words: Permafrost Regions, Expressway, Subgrade Fill Materials, Experimental Investigations